1. Field of the Invention
The techniques described herein are concerned with identifying specific wireless devices that are being used as triggers for weapons and distinguishing them from those being used by ordinary users for their intended purpose. The techniques interfere minimally with ordinary users and permit countermeasures for the weapons to be focused on neutralizing the wireless devices that are being used as triggers.
2. Description of Related Art
Wireless devices may be used as triggering devices for weapons such as explosive devices. A wireless device that is being used in this fashion may be in an idle mode awaiting an incoming call or be in a traffic (voice) mode awaiting signaling from another wireless device or land line phone that has placed a call to the triggering device. In the former case, a circuit that is connected to the triggering wireless device's audible ringer circuitry triggers the weapon when the triggering wireless device rings. In the latter case, the wireless device has a headset jack and is set to auto-answer a call; the audible output from the headset jack is connected to a DTMF (touchtone) detector that is sensitive to a sequence of digits akin to a personal identification number (or PIN)—where all but the last digit is used to arm the device and the last digit is the trigger. The method which uses the PIN is preferred for moving targets such as convoys or motorcades, because it affords much more precise timing and therefore targeting.
The prior art has many techniques for inventorying or engaging wireless devices in some operational area. These typically involve the creation of a false beacon, often termed herein a baiting beacon, that entices a wireless device to register with it and once the baiting beacon has gained control of the wireless device it may proceed to use any number of methods to identify and/or disable the wireless device. A fundamental limitation of these techniques is that they cannot determine from the interrogation alone whether a wireless device that is being interrogated is in fact a potential threat. Because this is the case, countermeasures against a possible threat generally require that all wireless phones in the operational area be disabled. Further, because potential threats cannot be determined from interrogation, there is no ability to engage a specific threatening wireless device in a timely fashion.
Another fundamental limitation is that prior art techniques for engaging wireless devices cannot deal with wireless devices that are in traffic state rather than idle state. Once the wireless device has entered the traffic state, it is no longer susceptible to interrogation other than by jamming the device outright to force it to drop the call and then interrogating it—in which case, the limitations on interrogation described above remain. The traffic state problem is further complicated by the fact that the signals of wireless devices that are in traffic mode are generally encrypted and comingled across some swath of spectrum, making simple energy detection techniques ineffective for distinguishing between threatening and nonthreatening wireless devices.
The techniques described herein provide solutions to the foregoing and other problems of the prior art and thereby make it possible to rapidly distinguish between ordinary wireless devices and potentially threatening wireless devices and to neutralize the potentially threatening wireless devices without significantly affecting wireless devices that are being used for their ordinary purposes.